Electric discharge device apparatus



April 7, 1953 B. D. BEDFORD 2,634,382

' ELECTRIC DISCHARGE DEVICE APPARATUS Filed Jan. 30, 1952 F'i g l.

I I :z i :5 9 P i i I 2 .L /5 E F I l 1 I, I i E i L "j t I I Inventor:

His Attor ngg.

Patented Apr. 7, 1953 UNITED STATES PATENT OFFICE Burnice I). Bediord, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application January 30, 1952, Serial No. 269,081

3 Claims. 1

My invention relates to improved electric arc discharge apparatus.

Electric arc discharge devices of the type including an anode, a mercury pool cathode, and means for initiating an arc discharge between the anode and cathode are Well known and have been widely used for the controlled transfer of currents of large magnitude from one circuit to another. These devices are characterized by unilateral conduction between the anode and cathode and, when provided with a suitable control electrode, may be rendered totally non-conductive during predetermined intervals independently of the anode voltage.

In some installations of devices of this character, considerable difliculty has been experienced by failure of the devices to maintain their unilaterally conductive characteristic or by failure of the control electrode to hold off initiation of conduction until the desired instant. My invention involves a discovery that much of this difiiculty is due to the presence of unsymmetrical magnetic fields within the discharge space caused by the current in the external circuits connected with the discharge path and the resultant effect of these magnetic fields on the formation of cathode spots on portions of the discharge device other than the cathode and at times other than those indicated by the control voltages applied to the tube.

Accordingly, my invention contemplates the provision of means for insuring that such unsymmetrical fields are not produced. To this end, I provide a conductive structure surrounding the tube envelope for conducting the current externally of the tube in a symmetrical manner with respect to the tube axis. In this way, any magnetic field produced by the external circuit is symmetrical about the tube axis and eliminates the difficulties previously described.

Further advantages and features of my invention will become apparent as the following description proceeds, reference being had to the accompanying drawing in which Fig. l is an elevational view of electric discharge apparatus embodying my invention; Fig. 2 is a top plan View of the apparatus of Fig. l; and Fig. 3 is an elevational view showing a modification of my invention.

Referring now to the drawing, I have shown my invention applied to an electric discharge device of the mercury pool type including a generally cylindrical metal envelope l containing a liquid pool cathode 2 at the lower end thereof. An anode 3 is supported in axially spaced and insulated relation with respect to the oathode by means of an anode supporting stud 4 suitably connected to an externally accessible cylindrical terminal 5. The terminal 5 is supported from the upper end of the envelope I in insulated relation by means of a cylindrical glass member 6 sealed between the lower edge of the terminal 5 and the upper edge of a metal eyelet 1 supported from the upper end of the tube envelope. It will be readily appreciated that the discharge device may also include a suitable arc initiating electrode and a suitable control electrode in accordance with usual prior art practices.

As previously indicated, I have discovered that in many installations, discharge devices of this type fail to remain unilaterally conductive, that is, they became subject to arc backs. Also, in those installations where a control electrode is used for delaying the initiation of the arc discharge for a predetermined instant after the anode has become positive there has been a tendency for the control electrode to lose control. I have found that in such installations, the external circuits connected with the principal electrodes are such that the discharge current flowing in those circuits produces unsymmetrical magnetic fields about the axis of the discharge device envelope. In accordance with my invention this is eliminated by providing a suitable conductive structure around the envelope of the discharge device which forms a part of the external circuit for the discharge current. As shown in Fig. 1, this structure comprises a plurality of longitudinally extending conductors 8, equally spaced about the exterior of the envelope wall and joined at the upper and lower ends to semi-circular members 9 and H! which are bolted together to clamp the conductive structure to the tube envelope. As illustrated in Fig. 2, the semi-circular conductors 9 at the upper end of the envelope l are insulated from the tube envelope by means of a lining of insulating material ll. Similar initiating material may be used to line the conductor It at the bottom of the envelope, if desired. It will be appreciated, however, that in those cases where the cathode is conductively connected to the envelope, the insulation may be omitted and the cathode current conducted directly to the conductors H).

In the embodiment shown in the drawing, the cathode 2 of the device is electrically connected with the lower end of the conductive structure 3 by conductors I 2 and [3 which are Joined to laterally extending terminals [4 provided on the semi-circular conductors [0. The external cathode circuit may be completed to a cathode bus by connection to terminals l5 provided on the semi-circular conductors 9 located at the upper end of the tube envelope.

With this constructon, the discharge current is conducted from the cathode through conductors l2 and I3 through the terminals I l and then divides between the four longitudinally extending conductors 8. It will be readily appreciated that with such a symmetrical arrangement, the magnetic fields produced by current flow in these conductors is symmetrical with respect to the axis of the discharge device envelope I and will not have any tendency to displace the are or cathode spot of the device toward the side wall of the envelope. The insulation H is provided to avoid any sparking that might tend to occur due to the low voltage that would result from current flow through the conductors B an the envelope of the discharge device.

In the modification, shown in Fig. l, the conductive structure terminates at the upper end of the tube envelope and while this has been found adequate in most cases, it is apparent that the structure may be extended above the tube envelope if desired. In Fig. 3 I have shown such a modification in which the conductive structure extends from the upper end of the envelope to the region of the anode terminal 5. It will be appreciated that the various parts illustrated in Fig. 3 correspond to similar parts in Fig. l and the corresponding parts have been designated by the same reference numerals. It will be appreci ated that no insulation is interposed between the tube envelope and the ring H1 in this modification.

Also, since in many discharge devices of this character the cathode is conductively connected with the tube envelope, it is possible to use the tube envelope for a part of the return path provided suitable conductive structure is provided for insuring a circumferential distribution of the return current. It will be apparent that the structure shown in Fig. 3 accomplishes this purpose and further extends the region in which the magnetic field is symmetrical with respect to the axis of the tube envelope for a substantial distance above the anode surface.

While I have described and claimed particular embodiments of my invention, it will be apparent to those skilled in the art that changes in modification may be made without departing from my invention in its broader aspects and I aim, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. The combination comprising an are discharge device including a generally cylindrical metal envelope, a mercury pool cathode within said envelope at one end thereof, an anode supported in axially spaced and insulated relation with respect to said cathode and a generally cylindrical conductive structure surrounding said envelope and conductively connected with said cathode and extending toward said anode to provide a return path for current from said cathode whereby a substantially symmetrical magnetic field is produced about the axis of said envelope by current in said conductive structure.

2. The combination comprising an are discharge device including a generally cylindrical metal envelope, a mercury pool cathode within said envelope at one end thereof, an anode supported in axially spaced and insulated relation with respect to said cathode and a generally cylindrical conductive structure surrounding said envelope and conductively connected with said cathode and extending toward said anode to provide a return path for current from said cathode, said conductive structure comprising a pair of ringlike conductors at opposite ends of said envelope and a plurality of equally spaced longitudinal conductors interconnecting said ring like con ductors.

3. The combination comprising an are discharge device including a generally cylindrical metal envelope, a mercury pool cathode within and in conductive relation to said envelope at the lower end thereof, an anode supported in axially spaced and insulated relation with respect to said cathode and means for producing a symmetrical magnetic field about the axis of said envelope comprising a plurality of longitudinally extending conductors equally spaced around said envelope and conductively connected with said cathode, said conductors extending toward the anode side of said cathode, and conductive means interconnecting said longitudinally extending con ductors to provide a return path for the discharge current.

BURNICE D. BEDFORD.

No references cited. 

